// TLE

#include <cassert>
#include <cmath>
#include <iostream>

long long solve(const long long x, const long long n) {
    long long ans = x;
    for (long long i = 1; i <= n; ++i) {
        if (ans <= 0) ans += i;
        else ans -= i;
    }
    return ans;
}

int main() {
    long long x, n;
    std::cin >> x >> n;
    std::cout << solve(x, n) << std::endl;
}